1. Technical Field
The present invention relates to an apparatus for inflating a vehicle occupant restraint, and particularly relates to an electrically actuatable initiator for an air bag inflator.
2. Description of the Prior Art
It is known to protect a vehicle occupant by an air bag that is inflated in the event of sudden vehicle deceleration such as occurs in a vehicle collision. The air bag restrains movement of the vehicle occupant during the collision. The air bag is inflated by inflation fluid from an inflator. The inflation fluid may be stored gas which is released from the inflator and/or gas generated by ignition of combustible gas generating material in the inflator. The inflator uses an electrically actuatable initiator to open the container to release the stored gas and/or to ignite the gas generating material.
The initiator typically includes a pyrotechnic ignition charge. The ignition charge may be electrically sensitive and may need to be insulated from stray electric currents or sparks to prevent inadvertent actuation of the ignition charge. In some initiators, the ignition charge is electrically insulated by an external layer of plastic which overlies an outer metal shell of the initiator. No internal electrical insulation of the ignition charge is provided. An external plastic film is susceptible to damage and, if damaged, may lose its electrical insulating capabilities.
The pyrotechnic material in an initiator may also be adversely affected by exposure to contaminants such as air or moisture. It is thus desirable to block the conduction of air, moisture, or other contaminants to pyrotechnic material within an initiator such as the ignition charge. This is typically done by welding together metal parts of the initiator, such as a cover and a base.